A digital camera, which is a type of mobile electronic unit, works on a fundamentally different concept than an existing film-type camera. The digital camera photographs a subject through an optical lens system and stores the corresponding photographed image information as digital data in a memory card. The digital data stored in the memory card can be processed in a desired format using a computer and can be easily transmitted via a network. Thus, the demand for digital cameras is expected to substantially increase.
The digital camera operates using power supplied from an AC adapter or a battery. A primary battery, such as an alkaline or lithium, and a secondary battery, such as a lithium-ion (Li-ion) or lithium hydrogen, have been widely used. A nominal voltage and an internal capacity of the secondary battery are higher than those of the primary battery, and thus, the secondary battery can guarantee a more stable operation in case of a low battery voltage. However, if the digital camera uses a current higher than a standard consumption current, such as during a flash check after Iris, shutter 1, and shutter 2 in a low battery voltage, the primary battery does not withstand the load. (In a camera with a two-stage shutter release, the shutter 1 mode operates by an ON signal of a first switch in a two-stage shutter release button for use in performing the camera's AE/AF operations and the shutter 2 mode operates by an ON signal of a second switch in the two-stage button arrangement.) Thus, the operating stability of a variety of IC (integrated circuit) units, such as a digital signal processing unit and a microcontroller of the digital camera, cannot be guaranteed, and communication errors between the IC units occur. In order to prevent the digital camera from malfunctioning, the power should be cut off when low battery voltage is present.